1. Field
Example embodiments generally relate to an image fixing apparatus and an image forming apparatus, and more particularly to an image fixing apparatus utilizing electromagnetic induction heating system, which is used for an image forming apparatus such as printers, copying machines, facsimiles, etc.
2. Discussion of the Background
A use of background image fixing apparatus utilizing electromagnetic induction heating system reduces a rising time of an image forming apparatus and saves energy.
In a background image fixing apparatus, an electromagnetic induction heating system includes a support roller serving as a heat roller, an auxiliary fixing roller serving as a fixing roller, a fixing belt which is tightly stretched by the support roller and the auxiliary fixing roller, an induction-heating device that counters the support roller with the fixing belt therebetween, a pressing roller which is in contact with the fixing belt on the auxiliary fixing roller, etc. The induction-heating device includes a coil member (an excitation coil) that extends in a width direction of the fixing device (the direction perpendicular to the feeding direction of a recording medium), a core member, etc.
The fixing belt is heated at a position in which the fixing belt faces the induction-heating device. A toner image on a recording medium is conveyed to a position between the auxiliary fixing roller and the pressing roller, and heated by the fixing belt, resulting in fixation of the toner image on the recording medium. In more detail, applying the coil member with a high frequency alternate current causes a magnetic field around the coil member, thereby generating an eddy current near the surface of the support roller. The eddy current causes a Joule heat due to the resistance of the support roller itself. The fixing belt, which is tightly stretched by the support roller, is heated with the Joule heat. It is known that the background image fixing apparatus using such an electromagnetic induction heating system may increase the temperature (a fixing temperature) of a surface of the fixing belt to a predetermined temperature with small energy and in a short rising time.
Another background image fixing apparatus using an electromagnetic induction heating system includes core members which face the fixing belt while being located at both sides of the fixing belt. Each of the core members faces the fixing belt at the corresponding side of the fixing belt. This technology is used for the purpose of improving heat efficiency in the fixing belt.
Another background image fixing apparatus using an electromagnetic induction heating system controls the Curie point of core members (magnetic core) of an induction-heating part in the width direction of the core members. In more detail, the Curie points at both end portions of the core members in the width direction thereof are lower than the Curie point at the center portion thereof. This technology is used for the purpose of preventing a problem in that the temperature of the fixing belt at both end portions in the width direction thereof excessively increases when a recording medium of small size is fed.
Another background image fixing apparatus using an electromagnetic induction heating system includes a fixing roller having a first heat layer made of a magnetic material and a second heat layer made of a non-magnetic material. The purpose of this construction is to reduce deterioration of the bearing of the fixing roller (heating roller) due to heat of the shaft of the fixing roller. In more detail, the resistivity of the first heat layer is higher than that of the second heat layer. The thickness of the first heat layer is greater than that of the second heat layer. The second heat layer mainly generates heat and the first heat layer made of a magnetic material reduces the magnetic flux, which is emitted from a magnetic flux generating device and reaches the shaft of the fixing roller.